Integrated circuit design continues toward larger system or subsystem inclusion on a single silicon slab. The term "chip" is in common use to refer to the completed integrated circuit on a small silicon slab inside of a housing or package. As this trend continues, more and more sophisticated functions are being incorporated on a chip during its design. This trend has been further driven by the low cost, low power consumption and speed of CMOS structures so that almost any system which has a large enough market to justify the initial design costs is now being designed and supplied by these manufacturers who had earlier concentrated on manufacturing component type integrated circuits such as ROM, RAM, gates and registers.
As this trend has continued a great deal of the system design effort which was earlier being done by the manufacturer of end products has been moved to the chip designer and integrated circuit manufacturers.
In integrated circuit design there are many design constraints, one of the most important is the "pin out". Since a single high density integrated circuit die is generally on the order of one centimeter square, although it may contain hundreds of thousands of transistors and metal interconnections, there is only a limited area to which a self supporting wire lead can be connected to the chip without shorting together. This limits the number of integrated circuit input or output leads to approximately 200 with standard processing technology.
Accordingly, integrated circuit designers have to make many difficult decisions as to those discretionary functions will be taken out of the chip on a pin, i.e. in the "pin out" to be made available off chip. Included in this discretionary group are those signals providing system diagnostic functions. In the prior art, chip designers have had to decide how to share diagnostic functions and operational functions on a pin as well as how many pins to dedicate to diagnostics and which diagnostic signals were to be provided off chip through those pins. Network controller chips require so many required functions that discretionary diagnostics have been limited to only a few pins, i.e. 4-5. Accordingly, many diagnostic functions are not provided off chip on dedicated diagnostic pins and this has made trouble shooting and maintenance more difficult and expensive especially in those situations where the chip is interfacing with other equipment and the interconnecting chips and media could also be malfunctioning. In many instances diagnostic information, if it were available from the chip, could specifically isolate an off chip malfunction and avoid expensive downtime.
It is an object of this invention to increase the ability to obtain chip diagnostic information without increasing the pin out assigned to this function.
It is a still further object to provide users the ability to select the pin out diagnostic signals from a class of diagnostic signals.
It is a still further object to provide users the ability to program a chip with software to provide combinatorial logical functions to a selected class of diagnostic signals including delay and/or blinking functions in order to increase the users choice of diagnostic information without requiring a dedicated pin for each function.